A variety of wireless radio signal communication devices rely on antenna duplexing filters. Such filters provide band-pass filtering both for incoming signals read by radio receiver elements and for outgoing signals generated by transmitter elements.
For wireless handsets, antenna duplexers in the form of conductor-coated ceramic monoblocks have gained wide-spread acceptance. In the basic ceramic block duplexer design, resonators are formed by typically cylindrical passages, called through-holes, extending through a parallelepiped (i.e. rectangular) block. The block is substantially plated with a conductive material (i.e. metallized) on all but one of its six (outer) sides and on the inside walls formed by the resonator holes.
One of the two opposing sides containing through-hole openings is not fully metallized, but instead bears a metallization pattern designed to couple input and output signals through the series of resonators. This patterned side is conventionally labeled the top of the block, though the “top” designation may also be applied to the side opposite the surface mount contacts when referring to a filter in the board-mounted orientation. In some designs, the pattern may extend to sides of the block, where input/output electrodes are formed.
The reactive coupling between adjacent resonators is affected, at least to some extent, by the physical dimensions of each resonator, by the orientation of each resonator with respect to the other resonators, and by aspects of the top surface metallization pattern. Interactions of the electromagnetic fields within and around the block are complex and difficult to predict.
While early wireless handsets were designed to operate with a single wireless network standard, handsets are conventionally designed to operate with multiple networks. The various wireless networks worldwide operate over channels at differing frequencies. Conventional wireless handsets include filtering for communication signals in several different frequency passbands. A single antenna duplexer is rarely sufficient to provide the necessary handset filtering.
More recently, government initiatives have begun to require that wireless network operators be able to track and report the geographic location of handsets operating in the network. To provide this location tracking service, wireless telecommunications operators and designers have focused on the global positioning systems (GPS). In order to track location with GPS, wireless handsets must include additional receiver circuitry and related signal filtering at another frequency, e.g. 1575.42 MHz.
When combined, the frequency requirements of GPS-based location tracking and multi-network compatibility create particularly complicated filtering schemes for wireless telephone handsets. Handsets designed for use with multiple networks and GPS location tracking may include several filters and related antenna switching subcircuits.
There remains a need for more versatile filters that can simplify handset filtering schemes by reducing the number of physical components required for filtering multiple standards. This invention pertains to a ceramic block filter that provides three or more passbands in a single block, and is suitable for use with GPS filtering requirements.